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I don't think the idea that (idealized, camera) lenses focus light from distinct points in one plane (or at infinity) onto distinct points in another plane is '
by jameshart 2y ago
I don't think the idea that (idealized, camera) lenses focus light from distinct points in one plane (or at infinity) onto distinct points in another plane is 'completely wrong', but I'm open to being educated on my error.
A lens focuses light parallel to its axis onto its focal point; it focuses parallel light coming in off-axis to other points on the focal plane.
Alternatively, and equivalently, it focuses divergent light coming from common points on planes closer than infinity, onto matching points on other planes behind its focal plane.
- smallnamespace 2y agoLenses bring parallel rays of light (alternatively, light from infinitely far away) to the focal point. They don’t bring idealized points to points. One consequence is you can’t use lenses to bring anything to a temperature higher than the temperature of the source light. For example you can’t use lenses + moonlight to light things on fire. Here’s an HN thread going into the physics of it: https://news.ycombinator.com/item?id=18736700 https://news.ycombinator.com/item?id=18736700